In manufacturing semiconductor devices such as LSI and super-LSI or in manufacturing a liquid crystal display board or the like, a pattern is made by irradiating a light onto a semiconductor wafer or an original plate for liquid crystal, but if dust is attached to a photo mask or a reticle (hereinafter collectively referred to as “photo mask” for simplicity) which is used during the irradiation operation, the resulting pattern would have roughened edges or black stains on the base, which would lead to problems such as damaged dimensions, poor quality, and a deformed external appearance.
Thus, these works are usually performed in a cleanroom, but it is still not easy to keep the photo mask clean all the time. Therefore, a pellicle is attached to a surface of the photo mask as a dust-fender before light exposure is carried out. Under such circumstances, foreign substances do not directly adhere to the surface of the photo mask but adhere only to the pellicle film, and since this film is sufficiently remote from the photo mask surface if the photo focus is set on a lithography pattern on the photo mask, the foreign substances on the pellicle film fail to transfer their shadows on the photo mask and thus no longer become a cause for problems for the image transfer performance.
In general, a pellicle is made by adhering a transparent pellicle film made of a highly light transmitting material such as cellulose nitrate, cellulose acetate, fluorine-containing polymer and the like to one of the two annular end faces of a pellicle frame made of aluminum, stainless steel, polyethylene or the like, using as the glue either a solvent capable of dissolving the pellicle film, which is applied to said annular end face (hereinafter this face is called “upper end face”) and then air-dried before receiving the film (ref. IP Publication 1), or an adhesive such as acrylic resin, epoxy resin or the like (ref. IP Publication 2, IP Publication 3, and IP Publication 4). Further the other annular end face (hereinafter called “lower end face”) of the pellicle frame is covered with an agglutinant made of polybutene resin, polyvinyl acetate resin, acrylic resin, silicone resin or the like for attaching the pellicle frame to a photo mask, and over this agglutinant layer is laid a releasing layer (separator) to protect the agglutinant layer.
In a case wherein, after a pellicle such as the kind explained above is adhered to a face of a photo mask, a photo resist film formed on a semiconductor wafer or an original plate for making a liquid crystal panel is exposed to a light via the photo mask, foreign matter such as dust is caught on the pellicle surface and thus is prevented from reaching the surface of the photo mask so that it is possible to avoid the effect of the foreign particle such as dust if the exposure light is emitted in a manner such that the focus occurs on the plane of the pattern formed on the photo mask.
In recent years, the semiconductor devices and the liquid display board have undergone further heightening in integration and densification. Currently, a technology of forming a fine pattern having a density level of 32 nm on a photo resist film is on the verge of realization. Such patterning can be effectively achieved by improved technologies such as an immersion exposure method, wherein the space between the semiconductor wafer or the original plate for liquid crystal on one hand and the projection lenses on the other is filled with a liquid such as super pure water and the photo resist film is exposed to an argon fluoride (ArF) eximer laser, or the double exposure method, which uses a conventional argon fluoride (ArF) eximer laser, to which the photo resist film is exposed.
However, the next-generation semiconductor devices and the liquid display board are being demanded to have even denser patterning of a level of 10 nm or further, and the conventional exposure technology depending on an excimer laser no longer can be improved to answer such a high demand for making a dense pattern of the level of 10 nm or denser.
Now, as a most promising method for forming a pattern of a density of 10 nm or denser, an EUV exposure technology which uses an EUV light of a dominant wavelength of 13.5 mm is in the spotlight. To achieve a pattern formation on the density level of as high as 10 nm or denser on the photo resist film, it is necessary to solve the technical problems with regard to the choices of light source, photo resist, pellicle, etc., and with respect to light source and photo resist, considerable progress and various proposals have been made.
With respect to a pellicle that improves yields of semiconductor device products or liquid crystal displays, IP Publication 3, for example, discloses a silicon film of a thickness of 0.1-2.0 micrometers to act as the pellicle film for EUV lithography which is transparent and does not give rise to optical distortion; however there remain unsolved problems which have prevented realization of the EUV light exposure technology.